1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine or a printer and, more particularly, to an image forming apparatus having an openable and closable member forming a part of a casing of the image forming apparatus.
2. Description of the Related Art
It is preferable that an image forming apparatus having an openable and closable member forming a part of a casing thereof to be first partially opened by merely pressing a button before it is then fully opened manually to perform maintenance inside of the main body of the apparatus and to relieve jammed recording members. The reason for this two-step operation is that by partially opening the openable and closable member, it is easy for an operator to insert his hand between the openable and closable member and the rest of the casing, making it possible to easily and fully open the openable and closable member.
To form such a construction, biasing means for biasing the openable and closable member in a direction in which it is open, and locking means for latching or locking the openable and closable member to a casing, are required. (For purposes of convenience, the following discussion will use the word "locking and variations thereof to describe preferred embodiments of the disclosed invention") Automatic locking of the openable and closable member to a casing as a result of closing the openable and closable member makes the operation easy. Therefore, it is preferable that the locking mechanism be constructed so as to elastically bias the openable and closable member.
Specifically, as shown in FIG. 15, a lid member 51 (the openable and closable member) is mounted so as to be openable and closable with respect to the main body 50 of the apparatus by means of a shaft 52. A bar 53 is disposed in the lid member 51, and a locking member 54 for locking the bar 53 is disposed in the main body 50 of the apparatus. With this construction, when the lid member 51 is pushed down, causing the bar 53 to be pushed down below the locking member 54, the lid member 51 is locked by the locking member 54 which returns to its original position by the bias of a spring 55.
Also, a push-up member 57 for pushing up the bar 53 by means of the bias of a spring 56 is disposed in the main body of the apparatus. By pushing up the lid member 51 when the locking mechanism is released, a handhold is provided for an operator to open the lid member 51.
Recently in image forming apparatuses, the weight of the lid member 51 has increased as the apparatus has become enlarged and for recording to be performed at a high speed. Also, in some image forming apparatuses, recorded medium is ejected onto the lid member 51. In such a case, the weight of the lid member 51 increases even more. Therefore, it is required that the bias force of the spring 56 connected to the push-up member 57 be increased and the amount of push-up also be increased. However, the bias force of the spring 56 becomes a resistance force when the lid member 51 is closed. The greater the bias force is, the greater the resistance is when the lid member 51 is closed. In particular, when the lid member 51 is locked, even after the bar 53 runs beyond the locking member 54, the bar 53 causes the lid member 51 to be pushed downward even more, causing an overstroke. However, there is a problem in that if the bias force of the spring 56 is large, a large force is required for the overstroke, reducing the ease of opening and closing the lid member 51.